High temperature NiO rubbing seal material containing CuO and CaF{HD 2

ABSTRACT

Sealing member having a low coefficient of friction and good wear resistance at elevated temperatures, particularly when used as a rubbing seal against ceramic rotary regenerators in gas turbine engines. The sealing member is a sintered ceramic member made from a batch of nickel oxide, copper oxide, and combinations of CaF2 and SrF2, with a preferred analytical composition of 3462 weight percent NiO, 14-28 weight percent CaF2 and 24-38 weight percent CuO.

United States Patent Lachman Dec. 2, 1975 1 HIGH TEMPERATURE N10 RUBBING SEAL 3,746,352 7/1972 R210 CI 211 277 96 R MATERIAL CONTMNINP CUO AND CH2 FOREIGN PATENTS OR APPLICATIONS 1751 Inventor: Lachman, Coming, 278,938 11/1970 U.S.S.R 252/12 Assigneez Corning Glass w gi 47-13813 4/1972 Japan 252/12 N.Y. Primary ExaminerHelen M. McCarthy [22] Ffled' 1974 Attorney, Agent, or Firm-Barry S. Bissell; Richard N. [21] Appl. No.: 518,598 Wardell; Clarence R. Patty, Jr.

52] us. c1. 252/12; 106/63; 106/73,1; ABSTRACT 2 165/9; 252/12; 277/96 R Sealing member having a low coefficient of friction [51] Int. Cl. C04B 35/02; ClOM 5/02 and good wear resistance at elevated temperatures, [58] Fleld of Search 106/731, 63; 252/12; particularly when used as a rubbing sea] against 277/96; 165/9; 117/93" PF ramic rotary regenerators in gas turbine engines. The sealing member is a sintered ceramic member made [56] References cue! from a batch of nickel oxide, copper oxide, and com- UNITED STATES PATENTS binations of CaF and SrF with a preferred analytical 3,370,006 2/1968 Campbell 252/12 Composition of 34-62 Weight Percent NiO, 14-28 3,429,720 2/1969 Houston et a1. 252/12 X weight percent C215 and 2438 weight percent CuO. 3,481,715 12/1969 Whalen et a1. 1l7/93.l PF 3,659,861 5/1972 Rao et al 277 96 R 8 Clam, N0 Drawmgs HIGH TEMPERATURE NIO RUBBING SEAL MATERIAL CONTAINING CUO AND CAF BACKGROUND OF THE INVENTION Rotary regenerators for gas turbine engines are being made of ceramic and glass-ceramic materials capable of effective heat transfer at elevated temperature. In

particular, CERCOR cellular glass-ceramic regenerators, made by Corning Glass Works and chemically comprising beta-spodumene solid solution as the primary crystal phase, are being tested by the industry.

Sealing members must be used in the gas turbine engine to separate the counter current gas flow paths and to seal the periphery of the rotary regenerator. The sealing members are preferably in rubbing contact with the regenerator and therefore must have a low coefficient of friction and good wear resistance, as well as good sealing properties, at operating temperatures of at least about 750C. An additional requirement eliminates many carbides, metal oxides and other potential materials; that requirement being that seal materials should not significantly abrade or wear the ceramic regenerator.

The present invention presents a ceramic material with the requisites of a good seal material. Prior art patents presenting sealing materials akin to the present materials include US. Pat. Nos. 3,746,35 2. The former patent discloses, inter alia, flame-sprayed nickel oxide base coatings containing 5-2570 of Group Ila fluorides. The latter patent discloses a seal member comprisinga metal substrate and a flame-sprayed surface layer wherein, although not preferred, the surface layer may consist of a glaze producing material containing calcium fluoride and a matrix material of cuprous oxide. The present applicants have nowfound a series of sintered ceramic seal materials which are equal ;to or better than the prior art flame sprayedseal materials with respect to coefficient of friction and wear resistance. The sintered nature allows a more economically fabricated .seal than the 3 ,3 70,006 and.

flame sprayed variety, and a seal which can easily. be

made thick cnoughto outlastthe lifeof the turbine engine.

SUMMARY oi THE INVENTION The invention is a sintered ceramic sealing member for gas turbine engines of the type having ceramic ro-.

8-7670 NiO, 5-40%, CaF SrF or mixtures thereof,

and 10-52% CuO. Calcium fluoride is the preferred metal fluoride and the preferred compositional range is 34-62% NiO, 14-2892 CaF and 24-38% CuO. Seals made according to the broad composition range have coefficients of friction of less than about 0.40 or wear rates of less than about 0.0040 inches/ 1 ()0 hours (0.1 mm/100 hours) in the Applicant's tests. Seals with compositions within the narrower range have coefficients of friction of less than about 0.30 or wear rates of less than about 0.0010 inches/100 hours (0.025 mm/l00 hours).

Sintering temperatures of ceramic seals according to the invention should be generally below about 1 100C. in air, since a liquid phase forms above this temperaturc. The Applicant theorizes that the liquid is a (u OCu() cutectic. Firings can be made at slightly on the rubbing surface. In any event, it appears that this 6CuO.Cu O phase may be responsible for the better film forming properties of the NiO.CuO.CaF and Ni- O.CuO.SrF compositions, of the present invention,

both on the seal surface and on the regenerator surface.

This thin film surface yields lower friction and wear characteristics for the present CuO containing seal materials when rubbing against the ceramic regenerators.

Methods of fabricating the seals herein include conventional ceramic material processes but the preferred method is by dry pressing. The seal may also be ceramically bonded to a substrate, but in either case, the formed ceramic seal is mechanically fixed in the turbine engine in rubbing contact with the regenerative matrix. One possible assembly in a turbine engine which can be duplicated with the present sliding seals is shown in US. Pat. No. 3,647,228, assigned to the Ford Motor Company.

In the dry pressing method of fabrication, the raw material powders are batched according to the limits of the invention and are reduced in particle size by milling in a liquid medium with known binders and plasticizers. The batch is then dried, granulated and isostatically pressed. followed by calcination, preferably in ari oxygen atmosphere. The calcined material is subsequently reduced to 325 Tyler meshpowder, binder is added, and the mixture granulated. Seals or test specimens are then dry pressed and iso'stati'cally repressed at 20,000

" psi (1406 kg/cm fand'fired' at about 1050C., ag'ain preferably in anoxygen atmosphere.

DESCRIPTION OF THE PREFERRED I EMBODIMENT EXAMPLE I Samples for friction and wear testing were ,made according to the following procedure. A 400 grams batchof a mixtureof green'nickeloxide, CuO. and CaF or; SrF (in the percentages shown inTableIlwas milled for each sample composition in-a ball mill for 4 hours,

with about 200 "cc of 1,111 -trichlorethane-,. l2 gramsof Carbowax4000 (Dow Chemical Co. trademarkland 8' cc of ricinoleic acid.- Afterfrnilling; each batch'was' dried, granulated andh ydrostatically pressedat 20,000

r psi 1406 kg/cm The pressed bodies were calcined at 1000C. for about 6 hours in oxygen and thenreduced to 325 Tyler mesh particles. 3 weight percent of the disclosed C arbowax 4000 was added to the powder followed by granulation and screening of the powder through a 10 Tyler mesh screen. Test samples were dry pressed and then hydrostatically repressed at 20.000 psi (1406 kg/cm and fired at 1050C. for about 6 hours in an oxygen atmosphere.

Samples 0.4 inches by 2.5 inches by 0.25 inches thick (1 cm X 6.3 cm X 0.6 cm) were cut from the pressed bodies and tested for friction and wear against a CER- COR honeycomb regenerative matrix 760C The matrix was 9 inches (23 cm) in diameter and was driven at 50 RPM. The seal samples were mounted in a holder and forced against the face of the matrix such that the 3 pressure on the face of the seal sample was a constant 7 psi (0.5 kg/cm Measurement of the force necessary to prevent sample rotation was measured by a load cell in communication with a torque arm supporting the containing seals.

I claim: 1. A sintered ceramic sliding seal for contacting a cesample mounting means. Using the force to prevent ro- 5 ramic regenerator in a gas turbine engine analytically tation, the area of contact, and the applied load, the coconsisting essentially of, by weight, 876% N10, efficient of friction was calculated and reported in l52% CuO and 40% of a metal fluoride selected Table I. Wear rates were determined by direct mea- 1 from CaF SrF and combinations thereof. surement after the test run. 2. The sliding seal of claim 1 wherein the metal fluo- TABLE 1 Batch Composition (wt.%) Coefficient Wear Length of Sample N0. M0 CuO CaF SrF of Friction (11.) (mm/lOO hours) Test (hours) Values for frictional coefficients and wear rates for current flame sprayed NiO.CaF compositions for the ride is CaF I 7 same test are in the range of 0.30 and 0.0010 in- 3. The sliding seal of claim 1 analytically consisting ches/lOO hours (0.025 mm/lOO hours), respectively. essentially of 34-62% NiO, 24-38% CuO and 14-28% The flame-sprayed seal is, however, generally quite thin 35 of the selected metal fluoride. because of the time and expense necessary to lay down 4. The sliding seal of claim 3 wherein the metal fluothe material on the substrate whereas the sintered seal ride is CaF of the present invention may be made as thick as neces- 5. A sliding seal for contacting a ceramic regenerator sary to match the useful life of the turbine engine. in a gas turbine engine comprising a sintered product of The NiO-CuO-SrF sintered seals have properties a raw material batch consisting essentially of 8-76 quite similar to those of the NiO CuOCaF seals. ln weight percent NiO, l0-52 weight percent CuO and addition, the SrF containing seals are more hydration 5-40 weight percent of a metal fluoride selected from resistant and may therefore be more attractive. The ef- CaF SrF and mixtures thereof. fect of hydration can be dramatic in extreme cases 6; The sliding seal of claim 5 wherein the raw matewhere the seal can be reduced to powder. In a simurial batch consists essentially of 3462 weight percent lated test conducted by the applicant, both CaF and NiO, 24-38 weight percent CuO and l4-28 weight per- SrF were subjected to an air/steam mixture for 4 hours cent of the metal fluoride. at 800C. with the resulting products being analyzed for 7. The sliding seal of claim 6 wherein the metal fluophase changes. Both masses hydrolyzed, the CaF parride is CaF tially going to CaO and Ca(Ol-l) and the SrF to 8. The sliding seal of claim 6 wherein the sintering SrCO The SrCO however, is rather stable up to temperature of the raw material batch is less than about about l250C. whereas the Ca(Ol-l) decomposes at 1100C. about 545C. Therefore, under certain service condi- UNITED STATES PATENT OFFICE cerrr rcrw or COECWN PATEM? NO. 3,923,667

DATED December 2, 1975 IFiVEWOWS) Irwin M. Lachman rr s certrfred that error appears in the ab0verderrtifred patent and that said Letters Patent hen-by corrected as showrrbelow:

TABLE. I Column 3 X6 L. Move sample No. 7 up to align with rest of columns across.

mlzd this twenty-third 3y 0f March 1 976 igncd [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'PaIenIs and Trademarks 

1. A SINTERED CERAMIC SLIDING SEAL FOR CONTACTING A CERAMIC REGENERATOR IN A GAS TURBINE ENGINE ANALYTICALLY CONSISTING ESSENTIALLY OF, BY WEIGHT, 8-76% NIO, 10-52% CUO AND 5-40% OF A METAL FLUORIDE SELECTED FROM CAF2, SRF2 AND COMBINATIONS THEREOF.
 2. The sliding seal of claim 1 wherein the metal fluoride is CaF2.
 3. The sliding seal of claim 1 analytically consisting essentially of 34-62% NiO, 24-38% CuO and 14-28% of the selected metal fluoride.
 4. The sliding seal of claim 3 wherein the metal fluoride is CaF2.
 5. A sliding seal for contacting a ceramic regenerator in a gas turbine engine comprising a sintered product of a raw material batch consisting essentially of 8-76 weight percent NiO, 10-52 weight percent CuO and 5-40 weight percent of a metal fluoride selected from CaF2, SrF2 and mixtures thereof.
 6. The sliding seal of claim 5 wherein the raw material batch consists essentially of 34-62 weight percent NiO, 24-38 weight percent CuO and 14-28 weight percent of the metal fluoride.
 7. The sliding seal of claim 6 wherein the metal fluoride is CaF2.
 8. The sliding seal of claim 6 wherein the sintering temperature of the raw material batch is less than about 1100*C. 